Photoelectric tube and circuit



June 1, 19 3. A. M L. NICOLSON PHOTOELECTRIC TUBE AND CIRCUIT OriginalFiled Jan. 29, 1938 Curved Scan 7; zny General;-

INVENTOR ALEXANDER McLEAN NICOLSON ATTORNEY :tube. from a dark area ofthe scene to a lighter area,

Patented June 1, 1943 UNITED STATES ATNT' orgies PHOTOELECTRIC TUBE ANDCIRCUIT Alexander McLean Nicolson, New York, N. Y., as-

signor to Communication Patents, Inc., New York, N. Y., a corporation ofDelaware 5 Claims.

This invention relates to improvements in photosensitive devices of theclass whose elements include an anode, a cooperating lightsensitivecathode, and the interconnections therefor. More specifically theinvention relates to photoelectric tube arrangements of the type used intelevision systems, such as, for example, the system disclosed in myapplication filed July 7, 1930, Serial No. 466,079, now Patent No.2,108,827, dated February 22, 1938, although the invention is notlimited to that use. p

This application is a division of my application Serial No. 187,758,filed January 29, 1938, now Patent No. 2,220,115, dated November 5,1940, which is a division of my Patent No. 2,108,827.

In the system disclosed in Patent No. 2,108,827 the image of a distantor near scene is focused upon the cathode of a photoelectric tube havinga non-linear characteristic. The focusing of the image on the cathodecauses a steady total emission of electrons to the anode of the tube,and produces a steady electric current in the input circuit of thephotoelectric current amplifier. A scanning ray of light, produced inany well known manner, but preferably in the form of an electrodynamicare along electrode rails in a magnetic field, i. e., an actinic ray, isemployed for scanning the image on the cathode. Since the intensity ofthe light of the scamiing ray is substantially constant, variations inthe current output of the tube are obtained through the non-linearcharacteristic of the photoelectric Thus, when the scanning ray isshifted the current output of the tube will be greater.

This variation in current in accordance with the variations in light anddark areas of the scanned image will reproduce the image at a receivingstation. The definition of all areas of the reproduced image at thereceiving station is greatly enhanced, as well as the efficiency andrapidity of response of the system, by the use of the photoelectric tubearrangement of the present invention.

In accordance with the present invention. a circuit is provided for aphotoelectric tube arrangement having a non-linear characteristic. inwhich the cathode is translucent and will transmit light through it aswell as being able to hold the image of a scene projected thereon,intercepting sufficient light for that purpose. The

cathode is sensitized on its opposite surfaces for response to thecharacter of the light to be projected thereon, one surface beingadapted to be position by thumb-screw Hi.

responsive to the spectrum light of the image projected thereon, and theopposite surface being adapted to be responsive to the scanning ray,which preferably is actinic, the cathode being translucent to bothoptical functions. An anode is positioned adjacent each surface of thecathode and the anodes are so constructed as not to materially interceptthe projection of theimage light or the scanning light on thecorresponding surfaces of the cathode. Since the distance between thesource of the scanning ray and the cathode is short because of spacerequirements, the cathode and the complementary anodes are preferablycurved about the source of the scanning ray, so that the scanning isuniform over every unit of area of the cathode and blurring of the imageat its borders, due to irregular scanning, as is common with flatcathodes, is avoided.

The output circuits of the cell in accordance with the present inventionare preferably ar ranged with a regenerative feed back coupling forincreased efficiency. Details of construction and further advantages ofthe photoelectric tube and the circuit of this invention will becomeapparent upon examination of the accompanying drawing, which is across-section of the tube and scanning arrangement with a diagram of theexternal electrical circuits. Referring to the drawing, numeral l0designates a camera casing divided into two chambers H and [2 by apartition l3. Chamber II contains a specially designed photoelectrictube i4 supported on a suitable base It: and locked thereon invertica-llyadjus'ted The chamber 12 contains an electrodynamic arcscreen i? supported on a suitable base l3 in which it is locked invertically adjusted position by thumb-screw 19. The screen ll ispositioned in alignment with tube I4 and a focusing lens'combination 20in the partition I3 directs the scanning ray from the screen ll on thetube M. A focusing lens combination 2! in the opposite wall of thechamber directs the image 0, such asthe scene to be transmitted, uponthe tube It.

The tube It comprises an evacuated or gasfilled transparent envelope ortube 22 containing a cathode 23 and symmetrically arranged anodes 24 and25 positioned on opposite sides of the cathode 23. The cathode 23 hasa'spherical curvature about the focus of the camera lens combination 2%]and the anodes 2t and 25 and the opposite surfaces of the envelope 22are complementarily curved as shown. The advantage'of the curved cathode23 isthat the projection path of the ray of light from the scanningscreen I! is always a constant distance from the cathode 23 and theimage thereon. In this manner the intensity of the normal light ismaintained constant at the image, so that a small and compact camera maybe provided without distortion of the image and out-of-focus blurring atthe borders, as is commonly the case with flat cathode tubes. The screenll thus may be fixed relatively to the cathode 23 for scanning all sortsof images.

The cathode 23 of the tubelfl is translucent and Will transmit lightthrough it as well as being able to hold the image of the sceneprojected thereon, intercepting sufficient light for that purpose. Theopposite surfaces oi-the cathode 23 are provided or coated with activelight-sensitive material, such as potassiumor the like, well known inthe art, the material on each cathode surface being responsive to thecharacter ofthe light projected thereon, and being con tinuous, i. e.,substantially uniformly conductive as compared to individual, insulatedphotosensitive cells The anodestE-i and 25 are so constructed, such as:of fine wire as shown, as not to materially. intercept the lightdirected on the opposite surfaces of the cathode, the light from theobject 0 being projected on the lefthancl side of the cathode 23, whilethe scanning ray of the screen I! is projected on the righthand sid ofthe .cathode, as seen in the drawings. The double anode arrangement withthe translucent cathode provides a very efiicient tube, as Well as anadvantageous arrangement from the mechanical point of view.

The screen 1'! produce a strong scanning ray of substantially constantintensityin anywell known manner, but preferably the ray is produced inthe form of an electrodynamic arc-along electrode rails 25 in a magneticfield producing actinic light as compared to the spectrum lightreflected from the object 3. Scanning systems of this natur are shown ingreater detail in my Patents Nos. 1,839,696 and 1,863,278. A shown inthe'drawing, a field winding 21, in series with the electrode rails 25,is provided for producing the magneticfield. This winding2l is enclosedin a jacket 28 packed with suitable heat dissipating material'23,such assteel wool or the like,

and containing a passage-33 through which a suitable heat-conductingfluid is circulated to maintain the screen electrode rails 2E at aconstant temperatureas well as for cooling the field winding '21. V

The external electricalcircuits which-embody the present inventioninclude a photoelectric tube amplifier having either two tubes, or asingle tube 3| with a double anode,-as shown. For example, the grid 32is connected to thecathode 23 of the photoelectric tub I l, while oneanode 24 of the tube I4 is connected through avariable inductance 33 toan anode 34 of the amplifier tube 3|. Similarly, the other anode 25 ofthe tube I4 is connected through a variable inductance 35 to the anode36 0f the amplifier tube 3!.

A variable resistance 37 is connected between the grid 32 and thefilament of the tube-3i for controlling th operation of the tube 14, andthe tube 3|. A plate potential 38 for the amplifier tube 3i, suppliesalso the operating voltage s for photoelectric tube l4 through theprimary of the output transformer 39, choke coils 49 and 4|, inparallel, the variable inductances 33 and 35 in parallel, tube anodes 24and 25 in parallel, cathode 23, and grid 32. It will beobserved thatt-wo interdependent regenerative circuits ar thus formed, one includingthe anode 24 and the cathode 23 and the other including the anode 25 andthe cathode 23.

An increase in electron emission of the cathode 23 to either of theanodes 24 or25 of the tube will produc an increase in the voltage of theinput circuit of the amplifier tube 3|, which will be transmittedthrough the output transformer 39 to a suitable amplifier 42. Thisoutput circuit has a tuning inductance 43 connected therein which isemployed for feed-back purposes and, with inductances 33 and 35, may beused to produce a certain amount of regeneration. With a circuit of thetype described above, the tube I 4 may be operated on alternatingcurrent thereby greatly simplifying th circuit and eliminating the needfor rectifying and filtering circuits.

The scanning electrode rails 26 and field coil 21 are supplied from asuitable scanning generator 44 through conductors 45. The output of theamplifier 42 is also-connected to conductors 45, for the purpose ofincreasing'the intensity of the scanning ray producing arc asthegphotoelectric tube l4 output currents are increased. This actionwill produce regeneration by. increasing the intensity of the scanningray in proportion to the increase in photoelectric'tube current. Thatis, should the tube output'current. be considerably increased by thescanning ray falling on a highly illuminated area of the cathode 23,this increase will be augmented by the substantiallysimultaneous-increase, in the scanning ray intensity. When the. rayfallson a less illuminated area, the contrastwill thus bemuch greaterthan with the normal scanning ray.

The photoelectric tub l4 output currents and the are producingcurrentsare segregated by a filter 46 in the output circuit of thesystem. The-output terminals 4'! may beconnected to suitabletransmission apparatus 48. The impulses from the scanning generator 44aretransmitted along with the photoelectric tube l4 output currents forsynchronizing the remote receiving screen with th transmitter 48. Withthe scanninggenerator 44 a direct current source, it is unnecessary .toemploy a filter.

The photoelectric tube. arrangement .of this invention isparticularly:adaptable:to.the television systemdescribed :in theaforementioned copending parent application. In sucha system,

the tube I4 is preferably disposed between the scen il being televisedand the scanning ray source ll. Since the cathode-23 is translucent,light refiected from the scene!) impinges on both sensitized surfaces,and lightfrom the scanning source IT also impinges onboth-sensitizedsurfaces, so that the efiiciency of conversion from radiant toelectrical energy'is much higher in this photoelectric tube than inother photoelectric cells used heretofore for this purpose.

It is evident that theeiiicienc'y; of this novel photoelectrictube'arra-ngement may be still further increased bycoating each side ofthe cathode with photosensitive material which is most sensitive to theluminous radiation falling on it; For example, in theabove-described'television"scanning system where visible lightisfocusedon one side of the. cathode anda scanning beam of actinicradiation is focused on the other. side of the cathode, the side of thecathodenearest the scene may be coated Withphotosensitive material whichis responsive to light fromthe sun or any artificiallighting ystem, andthe side .nearestthe scanning source may be coated with materialespecially sensitive to actinic radiation.

Obviously, the use of a photoelectric tube with a translucent cathodeand its associated circuit is not limited to the television art, but iscapable of adaptation to many other fields in which the transmission oflight, either visible or invisible, through the cathode of aphotoelectric tube may be desirable. Furthermore, the novelphotoelectric tube and circuit are capable of modification in form anddetail, and are not to be limited in any way by the embodiment describedin the specification except as defined in the appended claims.

I claim:

1. In a photoelectric device, the combination of a photoelectric cellhaving a non-linear characteristic and including a translucent cathode,photosensitive material on the opposite surfaces of said cathode, thesaid material on one surface of said cathode being activated byradiations of the visible spectrum, the said material on the oppositeside of said cathode being activated by actinic radiations, andamplifying means electrically connected to said cathode and responsiveto the activation of said material.

2. In a photoelectric device, the combination of a photoelectric cellhaving a non-linear characteristic, a cathode pervious to radiations inthe visible spectrum and actinic radiations, photosensitive material onsaid cathode adapted to be activated by radiations directed on oppositesides of said cathode, an anode spaced in cooperative electronicrelation to each of said opposite surfaces of said cathode and tworegenerative circuits, responsive to activation of said photosensitivematerial each including said cathode and one of said anodes.

3. In a photoelectric device, the combination of photosensitive tubehaving a non-linear characteristic and including a cathode pervious toactinic radiations and radiations in the visible spectrum,photosensitive material on said cathode adapted to be activated byradiations directed on opposite sides of said cathode, an anode spacedin cooperative electronic relation to each of said opposite surfaces ofsaid cathode and two regenerative circuits responsive to activation ofsaid photosensitive material, each including said cathode, one of saidanodes and a variable inductance.

4. In a photoelectric device, the combination of photosensitive tubehaving a non-linear characteristic and including a cathode pervious toactinic radiations and radiations in the visible spectrum,photosensitive material on said cathode adapted to be activated byradiations directed on opposite sides of said cathode, an anode spacedin cooperative electronic relation to each of said opposite surfaces ofsaid cathode, a vacuum tube having a filament, two anodes and a pair ofgrids interposed between said filament and said anodes, one electricalconnection including a variable inductance between one anode of saidphotosensitive tube and one anode of said vacuum tube, anotherelectrical connection including a variable inductance between the otheranodes of said tubes and an electrical connection between said cathodeand said grids.

5. In a photoelectric device, the combination of a photoelectric cellhaving a non-linear characteristic and including a cathode pervious toradiations in the visible spectrum and actinic radiations and having apair of opposite surfaces, photosensitive material on said cathode,adapted to be activated by radiations directed on either of saidopposite surfaces of said cathode, an anode spaced in cooperativeelectronic relation to each of said opposite surfaces of said cathodeand on opposite sides of said cathode, and electrical connectionsincluding said cathode and anodes and responsive to said activation ofsaid photosensitive material, said electrical connections including aregenerative circuit.

ALEXANDER MCLEAN NICOLSON.

